Hello all. I'm a fairly new member here, although some of you will know me from other forums and IRL visits.

I've had to put aside my turbocharged cars and work in my mom's 89 LeSabre. I'll start with the backstory and then get to the MAF questions.

While I was out of town, the LeSabre developed a no power and stalling problem with my mom. She took it to a local shop against my advice. They worked on the car for 2 days and when she picked it up, it didn't run 5 miles. She had it towed back, and they kept it another 2 days. This time it didn't make it 1 mile.

I met mom by the side of the road, and drove the car home by disconnecting the MAF sensor.

Once at home, I had a used MAF from a project car. With this one, the car would run and the stalling and bogging problem was gone. Now, the problem was hard starting and high idle. After checking around, I found the IAC motor was mounted with only 1 screw, and the pintle was overextended and bent. Looks like those idiots ruined it during their troubleshooting.

After installing a new IAC, the engine speed would flare up and settle back down after startup, like it should. However, it still had a high idle after it was warm. Laptop showed 0 IAC counts. I found that the shop had monkeyed with the minimum air screw on the throttle body, trying to get it to idle with a jammed-closed IAC. What losers!!! So, after adjusting this - the car is running very well... for the most part. At high RPM at WOT it had a breakup.

The car needed a tune-up, so I installed a new fuel filter and new spark plugs. The ignition coils all ohm out at 12KΩ each, and the ignition wires all are in the 6 to 8 KΩ range.

I installed a mechanical fuel pressure gauge and verified fuel pressure rises with manifold pressure, and holds about 43 PSI at WOT.

Since I want a NEW and original MAF, I ordered a Delphi from Rock Auto. I installed this in place of the junkyard MAF and immediately the engine developed a new problem. Any time I accelerated the engine above about 2500 RPM, it would break up, bog, and pop. Reading the MAF on the laptop, the reading would go from 75 Gm/Sec down to 12-13 during the bog. At lower speeds, the MAF performed perfectly. During this event the O2 sensor voltage would go to 0.05V (dead lean)

So, I went back to the junkyard MAF. With it, the engine will rev to 4800 RPM or so, at which time it falls on its face. Using the laptop, I see the MAF readings get to 120 to 130, then fall back to 80 or 90 when the bog happens. Oxygen sensor shows dead lean during the bog.

I have tried two different ECM's (one has emulator) and they both run exactly the same.

The engine has about 100,000 miles on the rebuild, and 450,000 miles total on the engine. It sounds perfect and runs perfect other than the WOT breakup. The heads have been lightly ported and compression bumped up slightly during rebuild. The engine has not had this problem for the first (at least) 50,000 miles. I haven't driven it in a long time so I don't know if the high RPM WOT breakup has been existing, or if it has been caused by the troubleshooting from the shop. My mom never runs the engine that hard so she would never notice. I am concerned that whatever is wrong will deteriorate and it may become a problem at less than WOT conditions.

Any ideas of where I should check? It appears the MAF measurement is dropping off when the breakup happens. I have tried two junkyard MAF's which both break up at the same point. The new Delphi MAF breaks up at low speeds and it appears to be clearly defective.

I have sworn off the so-called "Remanufactured" MAF sensors because of the awful quality. The picture below is what I found inside a "remanufactured" MAF. They have cut off the cover over the board, leaving shavings in the protective gel which can migrate through the gel and short the board. Also, the soldering quality is atrocious. This MAF is the one which was on the car. It had run for about 2 years.


The one I got from junkyard is an unbastardized Hitachi unit. This is it.


I ordered this new unit from Delphi, and it looks OK but the thermistors are different, and one of them is not the same type that the original MAF used.


New Delphi sensor probe:


Original type probe:


Once again, any insight would be very helpful. I do not have a lot of MAF experience. All of my turbo builds have been with speed density systems. This car with MAF has been extremely reliable and I haven't had to work on it much. I need to solve the WOT breakup problem. Open to any advice. Thanks in advance!

Sincerely,
David

I would go with the junkyard unit, since you seem to be having the best results with it, and give it a good cleaning (MAF Spray is a good start). Also, does the car still have the MAF screen installed? Finally, what does the o2 readings look like when the MAF is unplugged, or can you still see them?

_________________
~Randall~


1993 Buick Park Avenue - 197k - Some odds and ends done - Simply won't die
1994 Buick Regal - 78k - Bone stock - Always ready for a good kicking
1990 Oldsmobile 88 - Gone to a better place

Hi Randall. Thanks for the reply. Tomorrow I will check O2 with MAF unplugged, I didn't have laptop connected when driving it like that.

This early system really depends on the MAF as there is no MAP sensor. It runs alpha-N and is very badly impaired without MAF so I expect it will not run well at all at high revvs.

The screen is still in place, and undamaged. Will clean the sensor elements and see how much better it is.

Sincerely,
David

I guess the main concern with the unplugging of the maf was that of exhaust back pressure.

Either the MAF is reading wrong, or it's correct and flow is dropping less than what it was even before the issue crops up.

_________________
~Randall~


1993 Buick Park Avenue - 197k - Some odds and ends done - Simply won't die
1994 Buick Regal - 78k - Bone stock - Always ready for a good kicking
1990 Oldsmobile 88 - Gone to a better place

The other possibility is the wiring/connector. Normally wouldn't be an issue but if the shop it was at was as much of a hack as you suspect, they may have tried to re-wire something incorrectly.

_________________
Boost addict


The Fleet:
'93 SSEi - Twincharged + manual Build thread
'97 Camaro - Top swap
'05 STS - V8, AWD, her DD
'92 Trofeo - Fair weather DD
'99 Montana - top swap 3800
'04 Sierra 2500HD - LLY Duramax

Current project:
Something cool, trust me.

Upcoming projects:
'92 Bonneville SSE
'87 LeSabre T-type
'67 LeSabre

Gone to greener pastures:
'84 Sierra Classic - Twin turbo 3800
'97 LeSabre - Top swap

RIP:
'86 LeSabre - pictures
'93 SE - L67

It may be the high speed misfire is ignition rather than fuel system related.
Plug wires breaking down or a bad coil are two possibilities. How old are they?, showing the correct resistance doesn't necessarily mean all is well with the wires.
It's fair to say that you have some kind of issue with the fuel system, but it may not be the only problem you have.

Roger.

The Delphi MAF could be a revised design. Never had a problem with the OEM, just clean and good to go.

_________________
90 SSE Bonneville Sold but not forgotten.

Good point about checking wiring. I have about 0.4Ω resistance between the MAF power negative terminal and the engine ground. Also there is about 0.8Ω between the MAF power positive and the battery positive cable (with key on and battery disconnected). The MAF signal wire ohms out good between the MAF connector and ECM, and the wire insulation resistance is more than 200MΩ at 500V, using a Megger. So that rules out wiring. Thank goodness.

So today I replaced the ignition wires (because I had a set here already) and drove the car around about 50 miles.

The high RPM breakup is still there, but all other aspects of the engine performance are perfect.

When I get the replacement MAF from Rock Auto, I will install it and see what happens. I think the currently installed MAF is working fine, honestly.

On another car, I had similar high RPM breakup problem and it was ignition related. It was on a speed-density car, so there was no way it was MAF problem. I installed a Delco Type II ignition system and the problems went away.

Due to upcoming work obligation, it will have to be good enough for now. When I get home from work, I hope to install the Delco Type II unit.

Sincerely,
David